Bacterial Growth and Nutrition

1. 1
Bacterial Growth and Nutrition
• Bacterial nutrition and culture media
• Chemical and physical factors affecting growth
• The nature of bacterial growth
• Methods for measuring population size
http://diverge.hunter.cuny.edu/~weigang/Images/0611_binaryfission_1.jpg

2. 2
The First Law of Thermodynamics
• Energy cannot be created or destroyed.
– It is interchangeable with matter.
– Chemical energy; nuclear energy: E = mc2
• In order to grow, bacteria need a source of raw
materials and energy
– Source can be the same (e.g. glucose) or different
(e.g. carbon dioxide and sunlight).
– Living things can’t turn energy into raw materials,
only use it to assemble raw materials.
– Bacteria can’t grow on nothing!

3. 3
Where do raw materials come from?
• Bacteria acquire energy from oxidation of organic or
inorganic molecules, or from sunlight.
• Growth requires raw materials: some form of carbon.
• Autotrophs vs. heterotrophs
– Auto=self; hetero=other; troph=feeding.
– Autotrophs use carbon dioxide
– Heterotrophs use pre-formed organic compounds
(molecules made by other living things).
– Humans and medically important bacteria are
heterotrophs.

4. 4
Essentials of Bacterial nutrition
• Macronutrients: needed in larger amounts
– Needed in large quantities: CHONPS
• Carbon, hydrogen, oxygen, nitrogen,
phosphorous, and sulfur. H and O are common.
Sources of C, N, P, and S must also be provided.
– Macronutrients needed in smaller amounts:
• Mineral salts such as Ca+2
, Fe+3
, Mg+2
, K+
• Micronutrients = trace elements;
– needed in very tiny amounts; e.g. Zn+2
, Mo+2
, Mn+2

5. 5Element % dry wgt Source
Carbon 50 organic compounds or CO2
Oxygen 20 H2
O, organic compounds, CO2
, and O2
Nitrogen 14 NH3
, NO3
, organic compounds, N2
Hydrogen 8 H2
O, organic compounds, H2
Phosphorus 3 inorganic phosphates (PO4
)
Sulfur 1
SO4
, H2
S, So
, organic sulfur
compounds
Potassium 1 Potassium salts
Magnesium 0.5 Magnesium salts
Calcium 0.5 Calcium salts
Iron 0.2 Iron salts
http://textbookofbacteriology.net/nutgro.html

6. 6
Chemical form must be appropriate
• Not all bacteria can use the same things
– Some molecules cannot be transported in
– Enzymes for metabolizing it might not be present
– Chemical may be used, but more expensive
– These differences are used for identification
• Some chemicals are inert or physically
unusable
– Relatively few bacteria (and only bacteria) use N2
– Diamonds, graphite are carbon, but unusable
– P always in the form of phosphate

7. 7
Make it, or eat it?
• Some bacteria are remarkable, being able to
make all the organic compounds needed from a
single C source like glucose.
• For others:
– Vitamins, amino acids, blood, etc. added to a
culture medium are called growth factors.
– Bacteria that require a medium with various growth
factors or other components and are hard to grow
are referred to as fastidious.

8. 8
• Oligo means few; oligotrophs are adapted to life in
environments where nutrients are scarce
– For example, rivers, other clean water systems.
• Copio means abundant, as in “copious”
– The more nutrients, the better.
– Medically important bacteria are copiotrophs.
– Grow rapidly and easily in the lab.
Feast or famine: normal is what’s normal for
you:
Oligotrophs vs. copiotrophs

9. 9Responses of microbes to nutritional
deficiency
• Extracellular molecules collect nutrients
– Siderophores, hemolysins collect iron
– extracellular enzymes break down polymers
• Cells enter Semi-starvation state:
– slower metabolism, smaller size.
• Sporulation and “resting cells”:
– cells have very low metabolic rate
– Some cells change shape, develop thick coat
– Endospores form within cells; very resistant.
– Spores are for survival, triggered by low nutrients

10. 10
Endospore formation
http://www.microbe.org/art/endospore_cycle.jpg

11. 11Responses of microbes to other
environmental stresses
• Compatible solutes: small neutral molecules
accumulated in cytoplasm when external environment
is hypertonic.
• Heat shock proteins and other stress proteins
– Bacteria express additional genes that code for
protective proteins.
http://www.thermera.com/ima
ges/Betaine.gif

12. 12Culture Medium
• Defined vs. Complex
– Defined has known amounts of known chemicals.
– Complex: hydrolysates, extracts, etc.
• Exact chemical composition is not known.
• Selective and differential
– Selective media limits the growth of unwanted
microbes or allows growth of desired ones.
– Differential media enables “differentiation” between
different microbes.
– A medium can be both.

13. 13
Component grams
K2HPO4 0.10
KH2PO4 0.05
MgCl2 0.36
NaHCO3 0.05
{CaCl2 1 ml*
{BaCl2.2H2O
Na acetate 0.01
FeCl.7H2O 0.2 ml*
RNA 0.10
alanine 0.15
arginine 0.20
aspartic acid 0.30
glutamic acid 0.55
glycine 0.02
histidine 0.20
isoleucine 0.30
leucine 0.20
lysine 0.40
phenylalanine 0.30
proline 0.50
serine 0.30
threonine 0.50
valine 0.30
Defined Medium for Cytophagas/Flexibacters

14. 14
Physical requirements for growth
• Prefixes and suffixes:
• Bacteria are highly diverse in the
types of conditions they can grow in.
– Optimal or required conditions implied by
“-phile” meaning “love”
• Some bacteria prefer other
conditions, but can tolerate extremes
– Suffix “-tolerant”
• Note the difference!
http://www.kodak.com/global/images/en/health/filmImaging/thermometer.gif

15. 15
Oxygen: friend or foe?
• Early atmosphere of Earth had none
– First created by cyanobacteria using photosynthesis
– Iron everywhere rusted, then collected in
atmosphere
• Strong oxidizing agent
• Reacts with certain organic molecules,
produces free radicals and strong oxidizers :
– Singlet oxygen, H2O2(peroxide), O3
-
(superoxide), and
hydroxyl (OH-) radical.

16. 16
Protections of bacteria against oxygen
– Bacteria possess protective enzymes, catalase and
superoxide dismutase.
– Catalase breaks down hydrogen peroxide into water
and oxygen gas.
– Superoxide dismutase breaks superoxide down into
peroxide and oxygen gas.
– Anaerobes missing one or both; slow or no growth
in the presence of oxygen.
Fe3+
-SOD + O2
-
→ Fe2+
-SOD + O2
Fe2+
-SOD + O2
-
+ 2H+ → Fe 3+
-SOD + H2O2

17. 17
Relation to Oxygen
• Aerobes: use oxygen in
metabolism; obligate.
• Microaerophiles: require oxygen
(also obligate), but in small
amounts.
• Anaerobes: grow without
oxygen; SEE NEXT
•Capnophiles: require larger amounts of carbon dioxide
than are found normally in air.
A: aerobe
B: microaerophile

18. 18
Anaerobes grow without O2
• Classifications vary, but our
definitions:
– Obligate (strict) anaerobes:
killed or inhibited by
oxygen.
– Aerotolerant anaerobes: do
not use oxygen, but not
killed by it.
– Facultative anaerobes: can
grow with or without
oxygen
C: could be facultative
or aerotolerant.
D: strict anaerobe